Japanese Laid-Open Patent Application No. Sho-62-41521 discloses an apparatus for controlling a carburetor heater as shown in FIG. 1.
Referring to FIG. 1, an electro-magnetic pump 21 supplies kerosene from a fuel tank 22 through a fuel pipe 23 to a vaporizing chamber 25 of a carburetor 24. A heater 26 heats the carburetor 24, and a control means 27 controls the electric current flowing through the heater in accordance with the temperature level detected by a temperature sensor 28.
Further, a needle 29 opens and closes a nozzle hole 30, and a burner 31 is installed opposingly facing the nozzle hole 30, while there are installed an igniting plug 32 and a flame detector 35 on the top of the burner 31, the igniting plug 32 being for igniting the vaporized fuel, and the flame detector 35 being for detecting the ion current of the flames.
A judging means 33 which is connected to the temperature sensor 28 judges whether the pre-heated temperature as detected by the sensor 28 is higher than a pre-set igniting temperature. If the pre-set temperature of a power level setting means 34 is lower than the pre-heated temperature, the electric power setting means 34 lowers the power level supplied to the heater 26.
The above described conventional heater control apparatus can also be applied to a carburetor having the following burner structure.
As; shown in FIG. 2, the burner has a vaporizing chamber 41 for vaporizing the fuel, and has a mixing chamber 42 for mixing the vaporized fuel with air. These two chambers are separated by a mixing plate 44 having a communicating hole 43.
Further, an air supply tube 47 which is connected to a blowing fan 46 is installed at a lower side portion of a vaporizing wall 45 of the vaporizing chamber 41, while a fuel supply nozzle 48 is installed within the air supply tube 47.
Further, a flame hole 49 for forming flames is formed at an upper portion of the vaporizing chamber 41, while a heater 50 is embedded in the vaporizing wall 45 which separates the vaporizing chamber 41. Temperature sensors (not shown) are installed around the heater 50 to maintain the insulated state of the heater 50 and to detect the heat release of the heater 50, and these temperature sensors are embedded in the vaporizing wall 45 together with the heater 50.
The conventional carburetors described as above are controlled in the following manner.
In order to vaporize the fuel, the atmosphere within the vaporizing chamber has to be suitable for vaporizing, and this is achieved by pre-heating the heater.
That is, if an activating switch (not shown in FIG. 1) is turned on, the heater 26 is completely energized, thereby heating up the carburetor 24.
The temperature of the carburetor 24 is detected by the temperature sensor 28, while the control means 27 judges whether the data detected by the temperature sensor 28 indicates an ignitable temperature of the pre-determined level.
If it is found that the detected temperature has not reached an ignitable temperature, the control means 27 further completely energizes the heater 26, thereby heating the heater 26 further.
If the temperature detected by the temperature sensor 28 has reached an ignitable level, an ignition is carried out, and the electro-magnetic pump 21 is activated to supply the kerosene from the fuel tank 22 through the pipe 23 to the carburetor 24. The supplied fuel is heated and vaporized to be spurted through the nozzle hole 30.
Then the vaporized fuel sucks in ambiet primary air in order to use it for combustion, and this mixed gas is introduced into the burner 31. After the pre-heating, the igniting plug 32 which is installed on the burner 31 produces sparks to ignite the mixed gas.
After the ignition, the flame detector 35 detects the ion current of the flames, and, if the magnitude of the ion current reaches a pre-determined level, the control means 27 stops the spark discharge operation of the igniting plug 32.
Meanwhile, the temperature data detected by the temperature sensor 28 is inputted into a microcomputer (not shown) which is installed within the judging means 33. The microcomputer compares pre-stored temperature data (set at slightly lower than the igniting temperature) with the inputted data, and judges whether the temperature data from the temperature sensor 28 is higher than the pre-stored temperature data.
If the detected temperature is lower than the pre-set temperature, the judging means 33 supplies a control signal to the output level setting means 34, so that the output level setting means 34 should control the input power to fully energize the heater 26.
Thereafter, if it is found that the detected temperature is higher than the pre-set temperature, the power level setting means 34 curtails the amount of the input power for the heater 26 for example by 50 so that the temperature within the carburetor 24 should be maintained at a constant level. Then after the carrying out the igniting operation, the AC power supplied to the heater 26 is withheld.
That is, as shown in FIG. 1 in the conventional carburetor 24 26, when driving the heater, the temperature sensor 28 which is installed adjacent to the heater 26 simply detects the temperature of the heater 26, and, when the judging means 33 finds that the detected temperature has reached the pre-set temperature, the judging means 33 controls the AC power source to stop driving the heater 26.
Thereafter, when the temperature of the heater 26 reaches a lower limit of the pre-stored temperature data, the microcomputer turns the heater power section on again to resume the pre-heating operation of the carburetor 24.
Thus conventionally, the temperature of the heater 26 is varied between lower and upper limits, and therefore, the atmosphere within the burner 31 cannot be maintained in a perfect manner.
Further, even when the input electric power is withheld from the heater 26 during the heat release of the heater 26, the heater 26 raises the temperature above the temperature at the power disconnection, because of the latent heat in the material of the heater 26. On the other hand, when the heater 26 is disconnected from the power source for a certain period of time, even if the ac power supply is resumed, the heater 26 is cooled down to below the lower limit. Consequently, the atmosphere within the vaporizing chamber 25 becomes unstable, and therefore, the combustion becomes imperfect. In such a case, white smoke with the odor of kerosene is produced within the burner 31, thereby polluting the interior atmosphere of a room.